Not Applicable
Not Applicable
1. Field of the Invention
This invention relates to broadband communication networks, and particularly to cable television distribution systems.
2. Description of the Prior Art
A cable television distribution system is a species of broadband communication network in which subscriber connectivity is controlled through the use of radio frequency transmission line taps. Such taps are typically mounted on telephone poles or in ground-mounted housings where they are relatively inaccessible. Each tap usually has multiple ports that are each connectable to a lead-in cable or xe2x80x9cdropxe2x80x9d that extends from the tap port to a subscriber""s premises. By way of example, one tap may have four ports serving four subscribers, eight ports serving eight subscribers, and so on. In a typical cable television distribution system, there may be as many as one-half million or more subscribers requiring as many as one hundred and twenty-five thousand or more taps.
Traditionally, cable television subscriber connectivity is controlled by physically connecting and disconnecting the subscriber""s lead-in cable to and from the tap port. This operation requires that a cable company employee travel to the subscriber premises location and either utilize a power lift device, if the tap is mounted on a telephone pole, or a special key, if the tap is mounted inside a locked housing. In even a modest size cable television distribution system, the cost of such tap connection servicing can be quite high. Moreover, this scheme allows unauthorized cable connections to be made by those agile enough to climb telephone poles or resourceful enough to open the locks on cable housings.
As a response to this dilemma, a species of tap has been proposed that allows subscriber connectivity to be controlled remotely from the cable operator""s head end office. The ports in such taps remain connected to the subscriber premises lead-in cables, but the ports are switchable inside the tap via control signalling transmitted by the cable operator. Because each tap is assigned an address for distinguishing its control signals from other control signals generated for other taps, this species of tap is commonly referred to as an addressable tap.
A significant disadvantage of prior art addressable taps is that the message processing and switching circuitry incorporated into each tap must be powered by battery or by the transmission medium (cable plant) carrying the rf signals. Powering by battery is not desirable because batteries must be periodically replaced. Using line power is a better solution but is expensive because the power requirements of the tap circuitry exceed the power levels used to drive the rf signal amplifiers and other transmission line equipment. Thus, additional power supply equipment must be added to the cable plant.
Accordingly, there is a need in a broadband communication network for a system and a method of controlling subscriber access from a central location, without having to increase transmission line power levels. What is particularly required is an improved, low power addressable tap system for a cable television distribution system that facilitates head end control of subscriber connections using existing transmission line power supply resources.
A novel system and method are proposed for use in a broadband telecommunication network that includes a plurality of switching units, such as addressable taps, controlling subscriber access to the network. The inventive system and method solve the above-described problems by controlling the switching units from a central location using minimal network transmission medium power. In accordance with the inventive system and method, a repeating sequence of switching unit control messages is sent from the central location across the network. Each of the messages is addressed to an individual one of the switching units. Each switching unit is periodically powered up from a low power xe2x80x9csleepxe2x80x9d state to a higher power operational xe2x80x9cwakexe2x80x9d state in synchronization with a corresponding one of the control messages being sent from the central location. After each switching unit""s corresponding control message is processed, the switching unit is returned to its lower power sleep state.
In preferred embodiments of the invention, the broadband telecommunication network is a cable television distribution system including (1) a head end, (2) at least one transmission line carrying communications from the head end, and (3) a plurality of taps connected to the transmission line(s) and containing switchable ports connecting to cable subscribers. A tap record generating circuit is provided in the head end for generating a repeating sequence of tap records. Each tap record is addressed to a specific one of the taps and contains information for controlling the state of the port switches. A tap control circuit is provided in each of the taps. Each tap control circuit includes a low power stage and a higher power stage. The low power stage is configured to control the higher power stage by maintaining it in a sleep state until a corresponding tap record is about to be sent from the head end. The low power stage then wakes up the higher power stage so that it can process the tap record. The higher power stage is configured to read tap records as they arrive from the head end and to identify a corresponding tap record. The higher power stage processes the tap record and takes responsive action (e.g., setting the tap port switches) as necessary in accordance with the tap configuration information contained in the tap record. The higher power stage then calculates a time interval for reawakening and provides the time interval to the lower power stage, whereupon the higher power stage puts itself to sleep.